Temperature and pump power dependent photoluminescence characterization of MBE grown GaAsBi on GaAs

Bulk and quantum well GaAs_1?xBi_x/GaAs layers with Bi mole fractions from 0.02 to 0.10 are grown by molecular-beam epitaxy at temperatures ranging from 280 to 320?°C. The samples are characterized using temperature and pump-power dependent photoluminescence measurements covering 8–300?K and 1–250?mW (7–1,800?W/cm²), respectively. The results indicate that there is strong reduction in bandgap energy with the incorporation of small amounts of Bi and that GaAsBi most likely forms a weak type-I band alignment with GaAs.     

Classification of acute lymphoblastic leukaemia using hybrid hierarchical classifiers

Multimedia Tools and Applications - In current consequence of haematology, blood cancer i.e. acute lymphoblastic leukemia is very frequently founded in medical practice, which is characterized by...     

Ultrawideband Radar Measurements of Thickness of Snow Over Sea Ice

An accurate knowledge of snow thickness and its variability over sea ice is crucial in determining the overall polar heat and freshwater budget, which influences the global climate. Recently, algorithms have been developed to extract snow thicknesses from satellite passive microwave data. However, validation of these data over the large footprint of the passive microwave sensor has been a challenge. The only method used thus far has been with meter sticks during ship cruises. To address this problem, we developed an ultrawideband frequency-modulated continuous-wave radar to measure the snow thickness over sea ice. We synthesized a very linear chirp signal by using a phase-locked loop with a digitally generated chirp signal as a reference to obtain a fine-range resolution. The radar operates over the frequency range from 2-8 GHz. We made snow-thickness measurements over the Antarctic sea ice by operating the radar from a sled in September and October 2003. We performed radar measurements over 11 stations with varying snow thicknesses between 4 and 85 cm. We observed an excellent agreement between radar estimates of snow thickness with physical measurements, achieving a correlation coefficient of 0.95 and a vertical resolution of about 3 cm. Comparison of simulated radar waveforms using a simple transmission line model with the measurements confirms our expectations that echoes from snow-covered sea ice are dominated by reflections from air-snow and snow-ice interfaces.     

Model-based interpretation of ERS-1 SAR images of Arctic sea ice

Interpretation of Synthetic Aperture Radar (SAR) images of sea ice is complex because of the natural variability of sea ice and sensor-induced effects, such as speckle. Most of the research on SAR image interpretation has focused on the winter months and algorithms were developed to classify sea ice successfully under cold conditions. However, interpretation of SAR images during the seasonal transitions has proved difficult due to rapidly changing weather conditions. In this paper we address the application of SAR during the transition from summer to the fall freeze-up. This period is important because it signals the start of significant new ice growth, which affects the air-ocean heat exchange and injects brine into the upper layers of the ocean. We have interpreted SAR images of the sea ice in terms of the basic ice characteristics by using shipborne radar measurements of sea ice during the freeze-up and models derived from these measurements. We have shown that the model-based approach is effective in interpreting SAR images during this seasonal transition. This work also provides the physical mechanisms responsible for the large increase in backscatter observed at the end of the summer melt season.     

Temperature dependent luminescence in (Eu, Dy) doped tellurite glass

This short paper reports both the photoluminescence and the lifetime measurements of a prominent emission transition (⁵D₀→⁷F₂) of Eu³⁺ both in the presence and absence of the codopant rare earth ion (Dy³⁺) in an optical glass of the composition (79−x)TeO₂+6AlF₃+15LiF+xLn₂O₃ as a function of temperature down to 10 K.     

Enhanced near-infrared to green upconversion from Er3+-doped oxyfluoride glass and glass ceramics containing BaGdF5 nanocrystals

In this work, effect of glass composition as well as ceramization on visible and near-infrared (NIR) luminescence properties along with their decay dynamics of Er³⁺ ions has been compared considering two different oxyfluoride glasses yielding BaF₂ and BaGdF₅ nanocrystals. Both the glass systems have exhibited an intense normal and upconversion green emission under ultraviolet (378 nm) and NIR (978 nm) excitations, respectively. A remarkable enhancement of these emission intensities is observed for gadolinium-(Gd) containing glasses. Interestingly, NIR fluorescence intensity from Er³⁺ ions at 1540 nm has showed marginal decrease in gadolinium-containing glass which is attributed to occurrence of strong excited-state absorption (ESA) due to higher fluorine content ensuing an augmentation of upconversion green emission with a concomitant decrease in NIR emission. The quadratic dependence of upconversion green emission intensity on its pump power for all the samples revealed biphotonic absorption process from ground-state ⁴I_15/2 to the excited-state ⁴I_11/2 followed by ESA of second photon to the ⁴F_7/2 level. The intense green upconversion emission as well as enhanced NIR fluorescence lifetimes indicate the suitability of these glass/glass ceramics for upconversion lasers and amplification in the third telecom window.     

DISPERSION OF MATTER IN FLOW OF A BINGHAM PLASTIC IN A TUBE

The paper is concerned with the dispersion of a solute in a Bingham plastic fluid flowing in a pipe or a parallel plate channel. For pipe flow, the dispersion coefficient K₂ first increases with ξ₀ (the dimensionless radius of the plug flow region), reaches a maximum and then decreases. But in a channel flow, K₂ decreases monotonically with increasing ξ₀. Further K₂ for channel flow is found to be larger than that for pipe flow for all values of ξ₀ except 0.8≤ξ₀≤1.     

Mid‐IR transparent TeO2‐TiO2‐La2O3 glass and its crystallization behavior for photonic applications

In this report, effect of enhanced rare earth (La₂O₃) concentration on substitution of TeO₂ within ternary TeO₂‐TiO₂‐La₂O₃ (TTL) glass system has been studied with respect to its thermal, structural, mechanical, optical, and crystallization properties with an aim to achieve glass and glass‐ceramics having rare‐earth‐rich crystalline phase for nonlinear optical and infrared photonic applications. DSC analysis (10°C/min) demonstrates a progressive increase in glass‐transition temperature (T_g) from 359 to 452°C with the increase in La₂O₃ content. Continuous glass network modification with transformation of [TeO₄] to [TeO₃/TeO₃₊₁] units is evidenced from Raman spectra which is corroborated with XPS studies. While mechanical properties demonstrate enhancement of cross‐linking density in the network. These glasses exhibit optical transmission window extended from 0.4 to 6 μm with calculated zero dispersion wavelength (λ_ZDW) varying from 2.41 to 2.28 μm depending upon La₂O₃ content. Crystallization kinetics of TTL10 (80TeO₂‐10TiO₂‐10La₂O₃ in mol%) glass has been studied via established models. Activation energy (E_a) has been evaluated and dimensionality of crystal growth (m) suggests formation of surface crystals. Glass‐ceramic with crystalline phase of La₂Te₆O₁₅ has been realized in heat‐treated TTL10 glass samples (at 450°C). As predicted from DSC analysis, FESEM study unveils the formation of surface crystallized glass‐ceramics.